In a semiconductor device fabrication process, for example, as the surface of a semiconductor wafer should always be kept clean, a cleaning process is performed on the semiconductor wafer approximately. As a typical example of a single wafer type cleaning process of processing semiconductor wafers one by one, a process method is known which feeds a predetermined cleaning liquid to a semiconductor wafer held by a spin chuck (chemical liquid cleaning process), then feeds pure water to the semiconductor wafer to rinse the cleaning liquid (rinse process), and further rotates the semiconductor wafer at a high speed to spin the pure water off the semiconductor wafer (spin dry process).
Such a process method has a problem such that water marks is generated on the surface of a semiconductor wafer by adhesion of a mist of pure water, which is generated at the time of spin dry, to the dry surface of the semiconductor wafer, or the like.
As a cleaning method which suppresses generation of such water marks, Unexamined Japanese Patent Application Publication No. H4-287922 discloses a substrate processing method which comprises a cleaning process step of feeding a predetermined cleaning liquid to the surface of a substrate to be processed from obliquely above, a rinse process step of then feeding pure water to the surface of the substrate from obliquely above, and a dry process step of then rotating the substrate at a high speed to spin the liquid off, and overlaps the end period of the rinse process step and the start period each other, whereby a nitrogen gas is supplied to the center portion of the substrate in the overlap step and the dry process step.
Unexamined Japanese Patent Application Publication No. 2001-53051 discloses a substrate dry method which sprays an inactive gas to the center portion of a substrate after a rinse process, sprays pure water to the outer peripheral portion of the substrate, and moves the spray position of the inactive gas and the spray position of the pure water outward from the substrate in the radial direction.
As the semiconductor device fabrication process progresses, however, a pattern having a mixture of a hydrophilic surface (e.g., an SiO2 surface formed by a predetermined method) and a hydrophobic surface (e.g., a bare Si surface) is formed on the surface of the semiconductor wafer. Because the hydrophilic surface and the hydrophobic surface differ from each other in the water spin-off speed at the time of the spin dry process, the aforementioned conventional spin dry method has a difficulty in avoiding generation of water marks.